1. Field of the Invention
The present invention relates to a buffer memory control system for a swap system which processes an ordinary memory access only to a buffer memory and, when no data of a requested address exists in the buffer memory, moves out therefrom any one of blocks to a main memory and moves from the main memory into the buffer memory a block including data of the requested address. More particularly, the invention pertains to such a buffer memory control system for the swap system which is adapted so that when no data of the requested address exists in the buffer memory, the data is written directly in the buffer memory from the main memory under a specified condition.
2. Description of the Prior Art
In a conventional processor having a buffer memory and a main memory, when new data is to be written into the buffer memory, a tag is retrieved to decide whether needed data having a requested address is stored in the buffer memory and in the case of the needed data of the requested address existing in the buffer memory, a block including the needed data having the requested address is read out from the buffer memory and merged with the new write data and then written again in the buffer memory. In the case where the needed data of the requested address does not exist in the buffer memory, a replace block of the buffer memory which is located by a replace circuit is moved out to the main memory and then a block including the needed data of the requested address is read out from the main memory and merged with the new write data, thereafter being written in the buffer memory. That is, wherever the needed data of the requested address does not exist in the buffer memory, the block including the needed data of the requested address is moved into the buffer memory from the main memory.
Incidentally, in the processing of a write instruction (a block store instruction) for an area of a size equal to or an integral multiple of the block which is a basic storage unit of the buffer memory, since the entire block is rewritten, a part of the contents of the block is not of interest but is moved into the buffer memory from the main memory at that same time. Accordingly, in the processing of the write instruction the time for reading out the main memory generally corresponds to same loss of operation time. The swap system is disclosed, for example, in U.S. Pat. Nos. 3,771,137 and 3,848,234.